Fuel injection system



July 18, 1961 H. KNAPP 2,992,640

FUEL INJECTION SYSTEM Filed June 20, 1960 2 Sheets-Sheet 1 Fig.7

Y WKM July 18, 1961 H. KNAPP 2,992,640

FUEL INJECTION SYSTEM Filed June 20, 1960 2 Sheets-Sheet 2 F/g.3 1| 7 sec- 10 110 114 0 mm H9 I 1 I i 250 1000 2000 3000 n INVENTOR M444 M 8 United States Patent Ofi ce Patented July 18, 1961 2,992,640 FUEL INJECTION SYSTEM Heinrich Knapp, Stuttgart, Germany, assignor to Robert Bosch G.m.b.H., Stuttgart, Germany Filed June 20, 1960, Ser. No. 37,366 Claims priority, application Germany June 26, 1959 t 3 Claims. (Cl. 123-119) The present invention concerns a fuel injection system for internal combustion engines, and particularly for engines having air intake means and at least one electromagnetically actuatable fuel injection valve and electronic control means for actuating such valve or valves in a manner compatible with the varying operating conditions of the engine. In this type of a fuel injection system the individual valve is moved to open position by electric impulses applied to the electromagnetic valve control. The particular system to which the present application applies comprises at least two transistors influencing each other in opposite sense and therefore constituting a monostable flip-flop or multivibrator arrangement. For properly controlling the amount of fuel injected through the fuel injection valve during each actuation thereof a time control element is required in order to determine the duration of the individual impulses which cause the movement of the valve to open position. In order to assure an efiicient operation of the engine the amount of fuel injected by each valve into the associated cylinder for every stroke of the piston must be adjusted and controlled in proper relation to the amount of air sucked into the cylinder by the piston stroke so that the combustion of the fuel takes places without any excess of either fuel or air.

It is therefore a main object of this invention to provide in a fuel injection system of the type set forth time control means incorporating a device influencing the time control means in such a manner that the duration of the valve opening current impulses depends upon pressure variations in the air intake means of the engine.

It is a further object of the invention to provide time control means which are comparatively simple in structure and reliable in operation.

With the above objects in mind the invention provides in having air intake means and at least one electromagnetically actuatable fuel injection valve and electronic control means for actuating said valve by current impulses causing movement of the valve to open position, in coma fuel injection system for internal combustion engines bination, time control means for varying the duration of 1 the valve opening current impulses; and pressure sensitive means arranged to react to pressure variations in the air intake means of the engine, and for influencing said time control means to adjust the duration of said current impulses in a predetermined proportion to the pressures existing insaid air intake means.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration of an internal combustion engine and of the pertaining control arrangement according to the invention;

FIG. 2 is a schematic circuit diagram of the whole control arrangement including a diagrammatic illustration of one fuel injection valve;

FIG. 3 is a diagram illustrating the relation between the durations of the valve opening impulses with respect to different speeds of the engine and under various operating conditions thereof; and

FIG. 4 is a diagram illustrating the operation of the control arrangement according to the invention.

Referring now to FIG. 1, the engine 1.0 is equipped with a high-voltage ignition and with an electromagnetically controlled fuel injection system; of the high-voltage ignition system only the conventional high-voltage ignition distributor 11 is illustrated diagrammatically which comprises a rotating distributor switch arm 13 coupled with the crankshaft 12 of the engine for being rotated thereby, and cooperating with four stationary distributor electrodes or contacts 14. From each of these distributor electrodes an ignition cable 15 leads to one respective sparkplug 16 of the engine. For the sake of simplicity only one of these cable connections 15 is illustrated. The fuel injection system comprises four electromagnetically operated fuel injection valves 21 which are not illustrated in detail in FIG. 1. The individual injection valves are mounted in close proximity to'the not shown inlet valves of the engine, and more particularly Within the pertaining branches of the common intake manifold 22. Each of the valves 21 are supplied with the fuel which is to be injected into said branch of the manifold, through a respective fuel line 23 from a common storage tank 24. The fuel in the storage tank 24 is kept under practically uniform pressure by means of a pump 25 which is also electronic control arrangement 30 shown diagrammaticaL ly in FIG. 1 and in greater detail in FIG. 2. As can be seen further from FIG. 1, the individual solenoid coils in the individual fuel injection valves 21 are connected, via resistors 76, in parallel with each other, with the control arrangement 30, however in FIG. 2 the connection of only one of the coils 31 with the control circuit is illustrated for the sake of simplicity. The control arrangement 30 furnishes all of the valves 21 simultaneously with current impulses J the duration of which are so adjusted to the varying operating conditions of the engine that the amounts of fuel injected duringeach impulse from the valve housings into the air intake device result, in the subsequent combustion step in the cylinders, neither in excess of fuel nor in excess of air.

The entire control circuit arrangement illustrated by FIG. 2 is supplied with energy by the storage battery 32 which is otherwise also the source of energy for the highvoltage ignition system. The Whole circuit as shown one end with the negative terminal of the battery 32 and at its other end with the housing of the valve 21. The starting moment of the individual current impulses J applied to the coil 31 for opening the valve is determined by the rotation .of'a cam member 43 driven by means not shown in conjunction with the distributor switch arm 13 for rotation and actuating once during each rotation the movable switch arm 44 which is connected with the positive line,33 via a-resistor 46 of about 10,000 ohms, while the stationary contact 45 which cooperates with the arm 44 isconnected with the minus line '41. A condenser 48 of about .1; f isconnected, onjone side, with a junction point between the switch 44 and the resistor 46, and on the other side via a rectifier 49 and connection 50 with the base B of the transistor 35. This transistor 35 togethwith thetransistor36 constitutes, in view of the'c'on-' necions provided therefor as shown, a monostable flipflop arrangement. The emitter electrodes of these two transistors: are connected with each other, and are jointly connected via a common resistor 47 of about 50 ohms with the positive line 33; The two transistors 35 and 36 cooperate and influence each other'in such a manner that the normally non-conductive transistor 35 which is rendered conductive by the closing of the switch 43, 45 whereby the transistor 36 is rendered non-conductive, is returned to non-conductive condition by the transistor 36 after the latter has been returned to its normal conductive condition at the end of a delay interval determined by a time control device. The delay determining time control device comprises a choke coil 53 mounted on an ironcore 52, the inductance of the device being adjustable by meansof a displaceable yoke 54. According to the invention this yoke 54 is carried by a longitudinally shiftable control rod 55 diagrammatically illustrated in FIG. 2' and similarly in FIG. 1 Where it is connected with a diaphragm device 56 which, in turn, is connected with the intake manifold 22 of the engine. The movements of the not shown diaphragm of the device 56 control the movementsof the control rod 55 in such a manner that an air gap between the core 52 and the yoke 54 is increasedthe lower the pressure in the manifold 22 drops below atmospheric pressure. A series-combination comprising a resistor 60 and a rectifier diode 61 is connected in parallel with the coil 53 in such a manner that when the transistor 36 is in conductive condition no current can flow through the just mentioned series combination but only through the coil 53.

The collector of the transistor 36 is connected via a limiting resistor 65 with the base of the n-p-n transistor 34. The collector of the transistor 34 is connected across a resistor 66 with the positive line 33, and a junction point between the transistor 34 and'the resistor 66 is connected via another limiting resistor 67 with the base of the p-n-p transistor 37. The collector of this transistor 37 is connected via a resistor 68 with the negative line 41. A third limiting transistor 69 which otherwise is not important for the operation 'of the control device, is connected between the collector of the transistor 37 and the base of the transistor 38 which is also of the p-n-p type. The collector of the transistor 38 is connected via resistor 71.with" the negative line 41 while its emitter is connected via'a resistor 72 with the positive line 33. The emitter electrode of the transistor 38 is also connected with the base of'the transistor 39. The emitter potential of the latter is kept at a substantially uniform level by a germanium diode 74 which is connected in series with a resister 75 between the positive line 33 and the negative line 41. The just mentioned effect of the series combination 7 4; 75 is'due to the fact that even during non-conductive condition of the transistor 39 a substantial current is permitted to flow via the rectifier diode 74 and the resistor 75; Thecollector of the transistor 39 which is dimen sioned to carry substantial currents is connected via a plurality of decoupling resistors 76, respectively, with the individual solenoid coils 31 of the individual fuel injection valves 21. This is illustrated by FIG. 1 while in FIG. 2, as mentioned above, only one of the valves 21 and only 'onecoil 31 and only one resistor 76 are illustrated. A condenser 78 is connected in parallel with the coil 31 by a connection insulated from the housing of the valve '21 while the opposite end of the coil 31 is connected with the grounded housing of the valve andtherebywith'the negative line 41. The magnitude of the condenser '78 is so chosen with respect to the in-"' ductance o'f- -th'e solenoid coil 31 that the resonance'frc quen'cyideterniine'd by' theinductance of the coil 31 and the capacitance of the condenser 78 is approximately equal to the limit frequency of the eddy currents developing in the housing of the valve 21 upon excitation of the coil 31.

Finally, the above described circuit arrangement is supplemented by a transistor 40 the collector of which is directly connected with the negative line41 while itsbase is connected across a variable resistor 80 with a junction point between a condenser 81 connected to the collector of the transistor 38, and a resistor 82 connectedwith the positive line 33. The emitter of the transistor '40 is connected via a series combination of resistors 85 and 86 with the positive line 33. As will be described further below, the transistor 40 serves to control the amounts of fuel injected into the engine in a manner which depends upon the varying momentary rotary speeds of the engine. For this purpose two condensers 90 and 91 and two resistors 92 and 93 are provided as shown in FIG. 2. The condenser 90 is connected between the emitter of transistor 40 and the positive line 33, while the condenser 91 is connected between the positive line 33 and a junction point between the series-connected resistors 85 and 86. The

last mentioned junction point is furthermore connected with two Seriesconnected resistors 92 and 93', the last mentioned resistor being connected with the base B of the transistor 35.

In operation, as long as the switch arm 44 is in the shown open position the transistor 35 is non-conductive.

While a strong current J flows through the transistor 36 and the winding 53 of the iron core choke which produces in the'core 52 and in the yoke 54 a strongmagn'etic field. The potential a at the junction point A between the coil 53 and the rectifier diode 61 is determined under these conditions by the voltage division between the resistor 47 1 and the ohmic resistance of the coil '53 because during conductive condition of the transistor 36 the voltage difference between its emitter and its collector is negligibly small. In order to maintain the transistor 36 in conductive condition during the intervals between the closing periods of the switch 44, 45 and in order to return the transistor 36 to its'condu'ctive condition after each termination of one of the below described, control impulses acting on the fuel injection valves, a voltage divider arthe collector of the transistor 35 and the base of'the transistor 36, and the resistor '97 connected between the base of. the transistor 36 and the positive line 33. The b ase of'transistor 36 is connected with a. junction point between the resistors 96 and 97. The resistor 97 is so. dimensioned that during non-conductive condition of the.

transistor 35 the base potential of the transistor 36 is substantially lower than itsemitter potential. However,

the resistors 98 and 99 connected between the collector of transistor 36" or, more precisely,- between the junction 1 point A and the base of the control transistor 35 constitute a high ohmic resistance of such a magnitude that during conductive condition of the transistor 36 the potential. of the base B of the transistor 35 is somewhat higher than the potential of the two interconnected emitters of the transistors'35 and 36. In this manner the transistor 35 -is kept in non-conductive condition at the moment when in operation the switch 44, 45 is. closed which moment is the start of a cycle of operation. de scribed below.

As soon as the cam 43 rotating at half the rotary speed of the crankshaft 12 forces the switch arm 44 into engagemen-t'with the stationary contact 45 a control current is able to flow 'fromthe positive line 33 to the negative line 41.via the, emitter-base; circuit of the transistor 35, the rectifier 49 and the condenser 48 which acts like a short-circuit. This control. current renders the. emitter} collector or" f the transistor .35, ,'condnctive1 5 now" starting collector current Id of the control transistor 35 generates across the resistor 05 a voltage drop of such magnitude that the transistor 36 cannot be maintained in its conductive condition and the magnetizing current I which had been flowing through the choke coil 53 is greatly reduced. On account of the self-inductance of the choke coil 53 an induced voltage U appears in the choke coil 53 which tends to continue the above mentioned coil current I at its previous level. This generates a temporary current I flowing through the resistor 60, the rectifier diode 61 and the choke coil 53 whereby the potential at the junction point A becomes strongly negative with respect to the negative line 41. Hereby the n-p-n transistor 34 which was conducting is rendered non-conductive while the transistor 37 becomes strongly conductive and the transistors 3839 operating with phase equality relative to the transistor 35 become like wise conductive. The current I now starting to flow through the transistor 39 and the solenoid winding 31 of the valves 21 produces a magnetic field of suflicient strength to lift the valve cone 101 in each of the valves 21 from its seat in the nozzle 102 so that the fuel furnished under pressure through the lines 23 into the valve housing is able to issue from the nozzle 102 and to mix in the stream of air existing in the manifold 22 of the engine.

The duration of the current impulses I which maintain the valve cones 101 of the injection valve 21 in open position is determined by the inductance of the choke device comprising the Winding 53 and acting as a time control member. When the current I is terminated the decrease of the magnetic field produced in the iron parts of the core 52 and the yoke 54 is influenced by the current I so as to occur within a period of time partly determined by the magnitude of the resistor 60. During this time period the induced voltage U decreases and consequently the potential a at the junction point A rises slowly again to the potential of the negative line 41. Hereby also the potential b of the base B of the control transistor 35 is raised until finally it equals the value of the momentarily existing emitter bias voltage of the control transistor 35. In the diagram of FIG. 4 this moment is marked t and at this moment the control transistor 35 which had become conductive at the time t is again rendered nonconductive, While the meanwhile non-conductive transistor 36 returns to its original conductive condition and simultaneously renders the transistor 39 non-conductive so that the collector current I of the latter is terminated with a very steep flank whereby the valve cones 101 return, under the pressure of not shown return springs to their previous closing position with respect to the nozzle 102.

The above described cycle of operation is illustrated in FIG. 4 by the diagram curves a a and b 11 The curve a illustrates the variation with time of the potential at the junction point A, and the curve b illustrates the corresponding variation of the potential at the base B of the transistor 35 provided that-the pressure in the air intake manifold 22 of the engine is comparatively little below atmospheric pressure and that the inductance L of the choke winding 53 is large. The effect of a shift or displacement of the yoke 54 on the duration of the curent impulses J and thereby on the amounts of fuel injected upon each closing of the switch 44, 45 is illustrated by the curves a and 12 in FIG. 4 which are based on small values of the inductance L of the choke coil 53.

However, before further explaining this effect the relation between the amount of fuel injected and of the rotary speed of the engine and the pressure level in the airtake manifold below atmosphereic pressure will be explained in reference to FIG. 3. In this diagram curves 110-115 are shown as obtained by plotting above various abscissa points representing values of the rotary speeds n of the engine, as ordinates those impulars dura tionstg, which arenecessary to determine fuel amounts injected which would not result in the combustion in an excess of either fuel or air.

The curve applies to a condition of the engine in which it is operated at full load in which case the throttle 105, as shown in FIG. 1, provided within the air intake tube of the engine is positioned parallel with the axis of that tube so that the pressure within the mani fold 22 is only slightly below atmospheric pressure. In order to supply the engine under these circumstances with a sufiicient supply of fuel it is necessary to provide for the impulse currents I applied to the solenoid windings 3 1 of the valves an impulse duration t,, which increases from 5 msec. at 250 r.p.m. to 6.7 msec. at a speed n of 1500 r.p.m. It can be seen that from this point up to 2250 r.p.m. the line 110 is only slightly curved and drops thereafter to 5.8 msec. at 3,000 r.p.m.

The downwardly inclined portion of the line 110 is due to the fact that a speeds above 1500 r.p.m., the individual consecutive closings of the switch 44, 45 under the action of the cam 43 follow each other at increasingly shorter intervals so that with increasing speed the time available for setting up the required magnetic field in the choke device 52-54 is increasingly reduced. Accordingly, in FIG. 4 the line al ilustrates the variations in time of the potential at the junction point A, and the line a starts with a value existing at low speeds of the engine at the moment t when the switch 44, 45 is closed whereby, as explained above, the self-induction voltage U is generated. In the speed range between 0 and 1500 r.p.m. suflicient time is available for setting up the magnetic field mentioned above so that the self-induction voltage U which controls the potential at A reaches at every closing of the switch 44, 45 within this speed range the same value as indicated in FIG. 4. The base potential b of the transistor 35 is proportional to the potential a and thus drops from the moment t of closing the contacts 44, 45 with a time characteristic exponentially to the value 0, L indicating inductance of the choke device 52--54 at every respective moment, and R indicating the total resistance in the circuit portion comprising the elements 53, 60, 61. This resistance does not change substantially and is actually composed of the ohmic resistance of the winding 53, the resistance of resistor 60 and of the resistance of the diode 61 effective in the direction of the flow of the current J The transistor 35 is maintained in conductive condition from the moment t when the switch 44, 45 is closed, until the base potential b drops below the value of the potential U existing between the positive line 33 and the emitter of the transistor 35, i.e. when the transistor cannot be maintained anymore in its conductive condition. This moment at which the current impulse I applied to the solenoid windings 31 is terminated is indicated in FIG. 4 by r As has been mentioned above, at speeds above 1500 r.p.m. the magnetic field of the choke device 52-54 cannot be developed to its full normal value. Consequently, the coresponding self-induction voltage U appearing across the winding 53 decreases with increasing speed and the base potential b would reach the value of the emitter potential U at an earlier moment than before.

As is indicated in FIG. 3 by the line 110 the duration r of the current impulses should increase with increasing speed in the speed range starting with the idling speed of 250 r.p.m. and a medium speed of about 1500 r.p.m. This result is obtained by that portion of the circuit illustrated by FIG. 2. which concerns the transistor 40. This transistor is connected, as mentioned above, at its base via a condenser 81 with the collector of the output stage transistor 38 and can become conductive only when the transistor 38 returns to its non-conductive condition because then a short current is, capable of passing through the condenser 81 whereby the base of the transistor 40 is 7 made for a brief interval more negative with respect to its emitter. The current flowing toward the emitter of the transistor 49 passes through the resistors 86 and'85 and is stored by means of the smoothing condensers 90 and 91 during the intervals between the consecutive current impulses 1. Thus, a potential U is created across the resistor. 86 whereby the base potential of the transistor 35 is shifted in negative direction as indicated in FIG. 4. Hereby, the duration of the impulse J is extended by an amount At because the potential b at the base of the transistor 35 reaches, as the form of the line b shows, only at the moment t the voltage level 120 which is the level of the emitter-base potential difference reduced by the amount of the above mentioned voltage U Consequently, the duration I. increases up to a speed of 1500 rpm. in the manner indicated at 110 in FIG. 3, while beyond 1500 r.p.m. the above described influence of the incomplete generation of the magnetic field in the choke device 5254 increases and thereby compensates the extension At with increasing speeds.

Below iine 110, FIG. 3 shows four further characteristic curves illustrating the duration z of the current impulses depending upon variations of the difference between atmospheric pressure and the lower pressures existing in the air intake manifold 22. These differences are indicated at the right hand of the lines 110-115 in terms of mm. Hg. The lowermost line 112 applies to the condition that the engine o erates with substantially closed throttle 105 whereby a pressure of 400 mm. Hg below atmospheric pressure develops in the manifold and is eifective on the diaphragm device 56. As mentioned above, under such pressure conditions the diaphragm device 56 would pull by the connecting rod 55 the yoke 54 in the direction of the arrow I into a displaced position as illustrated in FIG. 2 whereby a considerable air gap between the yoke 54 and the iron core 52 is established. By the increase of this air gap, the inductance L of the choke device 5254 is considerably reduced. In accordance with the above given formula the time characteristic T is substantially reduced to an amount T and consequently the potential at the junction point A drops oif considerably faster which is illustrated by the dotted line a in FIG. 4. Consequently the base potential h of the transistor 35 reaches the value of the emitter bias potential U already at the time t The resulting duration z of the current impulse is, due to the reduction of the inductance L and the corresponding short ening of the time factor T, only very short and amounts, eg at an idling speed of 250 rpm, only 2 msee. As the speed increases, even at a pressure in the manifold 22 far below the atmospheric pressure a voltage U across the resistor 85 develops with increasing rotary speed of theengine; however, this voltage U causes a much smaller'extension Atg of the impulse duration'r because the curve- [2 intersects at a larger angle with the horizontal line 124) which represents the emitter bias potential reduced by the voltage U Since additionally the air gap between the yoke 54 and the iron core 52 adjusted in proportion to the drop of pressure in the manifold 22 causes a reduction of the inductance of the choke device 52'54, a shorter period of time is required for setting up the magnetic field. Under the operating conditions illustrated by line 110 in FIG. 3 i.e. with fully opened throttle,

the reduction of the time interval between consecutiveclosings of the switch 44, 45 has already at a speed of 1500 rpm. a considerable influence on the impulse duration t However, this influence is shifted toward increasinglyhigher rotary speeds the more the throttle 105 is moved into substantial closing positions whereby the difference between atmospheric pressure and the prevailing lower pressure in the manifold 22 increases This can be seen clearly from the diagram of FIG. 3 by comparing the curve 113 applying to a pressure difit'erential of mm. Mg with the curve 114 applying to a pressure differential of 200 mm. Hg and with the curve 115 applying to a pressure differential of 300 Hg, all these curves differing from the line 112 which is practically straight with slight rise while the portion of the curve in the area below 1500 r.p.m. has a much steeper rise.

A particular advantage of the above described control arrangement consists in the fact that only a diaphragm device is required as a pressure sensitive member by which the desired changes of the inductance L of the choke device 52-54 is produced depending upon the varying differentials between atmospheric pressure and the lower pressures appearing in the manifold 22 while the influence of the varying speeds of the engine on the required amounts of fuel to be injected is represented by an integration procedure in the electronic control arrangement.

Supplementary to the above described circuit arrangement two switches S and S may be provided of which the switch S in closed position short-circuits the adjustable resistor 99. The resulting extension of the duration of the control impulses I may be used in order to render the air-fuel mixture richer during the starting operation of the engine and for thereby facilitating the starting procedure. On the other hand, the switch S may be used for the purpose of substantially reducing the amounts of fuel injected when the engine is used as a brake while the vehicle is moved forward under its own momentum provided that the switch S is coupled with the control rod 55 by means not shown in the drawing. In this case one can arrange, in view of the very low pressure below atmospheric pressure as it develops when the engine is used as a brake, for causing the switch S to be closed from the moment on after the pressure in the manifold 22 has dropped'below a predetermined value because in this case the resistor 93 connected with the base of the transistor 35 would be short-circuited. Hereby the emitter bias potential of the transistor 35 caused by the output transistor 36 being in conductive condition is considerably reduced and thereby the duration of the unstable condition of the flip-flop is considerably reduced.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of fuel injection systems for internal combustion engines diifen'ng from the types described above.

While the invention has been illustrated and described as embodied in a fuel injection system for internal com bustion engines having at'least one electromagnetically actuatable fuel injectionvalve and electronic control means for actuating that valve, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis," the foregoing will so fully reveal the gist of the present invention that others can What is claimed as new and desired to be secured by Letters Patent is: I

1. In a fuelinjection system'fo'r internal combustion engines having air intake means and at least one electromagnetically actuatable-fuel injection valve and electronic control means including at least one monostable fl1p flop device changeable between a condition fors'tartln'g a current impulse and'a condition term'inating'said impulse,

for actuating said valve by causing movement of theyalve' H to open position through application of said impulse for the duration thereof, in combination, time control means including iron core choke means of variable inductance connected with the output of said flip-flop device for varying the duration of the valve opening current impulses, and an auxiliary circuit connected in parallel with said choke means and comprising a series-connection of a resistor and a rectifier so polarized that it constitutes a high resistance against an impulse current flowing through said choke means during the duration of said impulse, but permits free flow through said auxiliary circuit of a self-induction current generated in said choke means upon termination of said impulse; and pressure sensitive means including diaphragm means arranged in operative connection with said air intake means so as to react to pressure variations in the air intake means of the engine, and operatively connected with said choke means for influencing said time control means by variation of its inductance to adjust the duration of said current impulses in a predetermined proportion to the pressures existing in said air intake means.

2. A fuel injection system as claimed in claim 1, wherein said flip-flop device comprises an input transistor and an output transistor, at least one resistor being connected between the base of said input transistor and the collector of said output transistor, and an integrating means being connected in the emitter-base circuit of said input transistor for storing each of the current impulses as they are applied to said fuel injection valve.

3. A fuel injection system as claimed in claim 2, wherein said integrating means comprises two condensers and a series-combination of two resistors, one of said condensers being connected in paralel with said seriescombination of resistors, the other one of said condensers being connected in parallel with one of said two resistors of said series-combination, and a control transistor connected at its emitter with one end of said series combination of two resistors, the junction point between said two resistors being connected to the base of said input transistor, and a further condenser being connected between the base of said control transistor and a point of said control means Whose potential varies in synchronism with the application of said current impulses to said fuel injection valve means.

References Cited in the file of this patent UNITED STATES PATENTS 2,807,244 Barclay Sept. 24, 1957 

